1. Field of the Invention
The present invention relates to a motor drive circuit (hereinbelow called as motor driver) the circuit thereof and more particularly, relates to a small sized DC motor at a high torque and with a high efficiency, reduces noise generation and is suitable for forming in an I C/ and further relates to a motor drive system in which the circuit thereof is incorporated in a motor or mounted thereon.
2. Description of Related Art
FIG. 2 is a block diagram showing a conventional fan motor driver in an IC form which was mounted such as on an electronic device and a motor drive system including a fan motor driven thereby. The present example comprises a Hall element I fitted outside with respect to an IC, a fan motor driver 9 in an IC form which receives the output from the Hall element 1 and applies a drive current to a fan motor 8 in response to the received output and the fan motor 8 driven by the IC fan motor driver 9. A two phase DC brushless motor is usually used for the fan motor 8 (hereinbelow simply called motor 8). As such motor 8, a DC motor in which the stator thereof is provided with a coil which generates a rotating magnetic field and the rotor thereof is formed of a permanent magnet is generally employed. The Hall element 1 determines the rotating phase of the motor by detecting the magnetic field generated by the permanent magnet rotor. The motor driver 9 is provided with, within the IC, an amplifier 2 (hereinbelow abbreviated as AMP 2), a drive pulse generating circuit 3 and first and second drive circuits 4 and 5 which output a driving current to the motor 8. The AMP 2 amplifies the output signal from the Hall element 1 and outputs the same, and the drive pulse generating circuit 3 wave-shapes the output signal from the AMP 2 and outputs two drive pulses 4a and 5a (see (b) and (c) in FIG. 3) having a phase difference of 180.degree. each with respect to other and duties of about 50%. The first drive circuit 4 switches between being and not being electrically conductive between the external terminal 6 thereof and the grounding terminal in response to the drive pulse 4a received at its input side, namely, the first drive circuit 4 sinks the driving current supplied to the motor from the power source line +Vcc toward the grounding line via a so called switching operation. The second drive circuit 5 is a circuit performing the same operation as the first drive circuit, in that it forms the switching operation of electrical conduction and interruption between the external terminal 7 and the grounding line in response to the drive pulse 5a received at its input side.
More specifically, the first drive circuit 4 is composed of transistors Q11 and Q12 in Darlington connection, the collector of the transistor Q11 at the drive stage is connected to the external terminal 6 and the base thereof is adapted to receive the drive pulse 4a. The collector of the transistor Q12 at the output stage is connected to the external terminal 6, the base thereof is connected to the emitter of the transistor Q11 and the emitter thereof is connected to the grounding line. The first five circuit further comprises a zenor diode Z1 having the cathode connected to the external terminal 6 and the anode connected to the base of the transistor Q11. The second drive circuit 5 is likely composed of transistor Q13 and Q14 in Darlington connection. The collector of the transistor Q13 at the drive stage is connected to the external terminal 7 and the base thereof is adapted to receive the driving pulse 5a. The collector of the transistor Q14 at the output stage is connected to the external terminal 7, the base thereof is connected to the emitter of the transistor Q13 and the emitter thereof is connected to the grounding line. Like the first drive circuit 4, the second drive circuit 5 further comprises a zenor diode Z2 having the cathode connected to the external terminal 7 and the anode thereof connected to the base of the transistor Q13.
The operation of the conventional fan driver having the above constitution is explained hereinbelow with reference to the signal waveforms shown in FIG. 3.
In order to determine the phase of the fan motor rotor the output signal of the Hall element 1 is inputted to the AMP 2 and the amplified signal ((a) in FIG. 3) outputted by the AMP 2 is applied to the drive pulse generating circuit 3. The drive pulse generating circuit 3 wave-shapes the input signal from the AMP 2, for example by means of a logic circuit, corrects the phase thereof and generates two drive pulses 4a (see (b) in FIG. 3) and 5a (see (cl in FIG. 3) which differ in their phases by about 180.degree. from each other and have waveforms of inverted relation each other.
The drive pulse 4a is applied to the base of the transistor Q11 in the first drive circuit 4. The drive pulse 5a is applied to the base of the transistor Q13 in the second drive circuit 5. Now, in the first drive circuit 4 when the drive pulse 4a is at a HIGH level (hereinbelow indicated as "ON") the transistor Q12 is turned "ON" and the path between the external terminal 6 and the grounding line is rendered electrically conductive (see (d) in FIG. 3). As a result, a drive current from the power line +Vcc is supplied to one coil 8a of the two phase motor 8 and flows toward the external terminal 6. When the drive pulse 4a is at Low level (hereinbelow indicated as "OFF") the transistor Q12 is turned "OFF" and the path between the external terminal 6 and the grounding line is electrically interrupted (see (d) in FIG. 3). As a result, the drive current in the coil 8a is interrupted. Due to the disappearance of the drive current flow path at this moment a voltage induced in the coil 8a is applied to the zenor diode Z1 and when the voltage exceeds the breakdown voltage of the zenor diode the current flows therethrough and the energy thereof is dissipated thereat.
The operation of the second drive circuit 5 is the same as that of the first drive circuit 4 except that the phase of the input signal differs from that of the first drive circuit 4 by 180.degree.. When the drive pulse 5a is "ON", the transistor Q14 is turned "ON", therefore the path between the external terminal 7 and the grounding line is rendered electrically conductive (see (e) in FIG. 3). As a result, a drive current from the power source line +Vcc is supplied to the other coil 8b of the two phase motor 8, and flows toward the external terminal 7. When the drive pulse 5a is rendered "OFF", the transistor Q14 is turned "OFF", therefore, the path between the external terminal 7 and the grounding line is electrically interrupted (see (e) in FIG. 3). Thereby, the driving current in the coil 8b is interrupted and the current flowing in the coil 8b flows via the zenor diode Z2 and is dissipated thereat in the same manner as above.
As explained above, the fan motor driver 9 generates within the IC the two drive pulses 4a and 5a of which phases differ by 180.degree. from each other and alternately supplies the drive current to the two coils 8a and 8b of the motor 8 to rotate the rotor of the fan motor.
Because such IC motor driver is only rendered conductive &rom the external terminals 6 and 7 to the ground line, such DC motors are almost limited to the two phase DC motor. Further, in such driver the two motor coils have to be driven alternatively, and the generated motor torque is low in comparison with the size thereof to thereby lower the efficiency thereof. Still further, because the counter electromotive force generated in the motor coils is dissipated via the zenor diodes, noise is likely generated during the switching of the driving current, therefore in case that the fan motor was mounted on an electronic device there was a high possibility that such driver circuit adversely affected other circuits.
In order to reduce the internal temperature rise of electronic devices such motor driver and fan motor are generally mounted on the electronic devices, it is desired that such motor driver is formed in an IC and further the size thereof is desired as small as possible. Further, the power efficiency of the fan motor mounted on the electronic device is desired as high as possible. It is undesirable that power consumption of the fan motor is large since the circuits therefor are formed in a high integration and with a low power consumption.